The present invention relates to a process for producing an xcex1-aminohalomethylketone from an N-protected xcex1-amino acid ester with an amino group protected as an imine via a novel N-protected-xcex1-aminohalomethylketone.
Further, the invention relates to a process for producing an N-protected-xcex1-aminohalomethylketone, a xcex2-aminoalcohol, an N-protected-xcex2-aminoalcohol or an N-protected-xcex2-aminoepoxide derived from the xcex1-aminohalomethylketone.
Still further, the invention relates to an N-carbamate-protected-xcex1-aminohalomethylketone, an N-carbamate-protected-xcex2-aminoalcohol or an N-carbamate-protected-xcex2-aminoepoxide derived from the xcex1-aminohalomethylketone.
An xcex1-aminohalomethylketone (compound of formula (3) to be described later) and its salt can be converted into peptidylhalomethylketones by the method which is ordinarily used in the peptide synthesis, and they are compounds useful as intermediates for synthesis of various peptidylhalomethylketones which are known as serine protease inhibitors (refer to, for example, W. Brandt et al., Int. J. Peptide Protein Res. 1995, 46, 73).
In addition, they are reported to be useful as intermediates for synthesis of HIV protease inhibitors (refer to, for example, J. Med. Chem. 1990, 33, 1285).
Furthermore, an N-protected-xcex1-aminohalomethylketone (compound of formula (7) or (10) to be described later), a xcex2-aminoalcohol (compound of formula (13) to be described later) and an N-protected-xcex2-aminoalcohol (compound of formula (8), (11) or (14) to be described later) and an N-protected-xcex2-aminoepoxide (compound of formula (9), (12) or (15) to be described later) derived therefrom are likewise known to be important compounds as medical intermediates of HIV protease inhibitors.
An xcex1-aminohalomethylketone has been so far produced by deprotecting an N-protected-xcex1-aminohalomethylketone (refer to, for example, S. Fittkau et al., J. Prakt. Chem. 1986, 529).
As a method for producing N-protected-xcex1-aminohalomethylketones, for example, a method has been known in which N-protected xcex1-amino acid ester is reacted with a metallic enolate formed from an xcex1-haloacetic acid and decarboxylation is conducted (refer to WO 96/23756).
In this method, however, as described in Examples of WO 96/23756, a costly Grignard reagent or an organolithium reagent has to be used in an amount of more than approximately 4 equivalents based on N-protected amino acid ester.
A method is also known in which production is conducted such that an alanine ester having an amino group protected with a dibenzyl group is reacted with a halomethyllithium (refer to J. Barluenga et al., J. Chem. Soc., Chem. Commun. 1994, 969).
In this method, however, groups other than a dibenzyl group are not studied as a protecting group of the amino group, and a method in which elimination of the dibenzyl group is conducted while maintaining a halogenated ketone moiety is unknown. Thus, the method cannot be used as a method for producing an xcex1-aminohalomethylketone.
A method is also known in which production is conducted such that a carbamate site of an amino acid ester having an amino group protected with a carbamate group is further protected with a trialkylsilyl group, and then reacted with a halomethyllithium (refer to Japanese Patent Laid-Open Nos. 99,947/1996 and 99,959/1996).
Nevertheless, in this method also, as described in Examples of Japanese Patent Laid-Open Nos. 99,947/1996 and 99,959/1996, a costly organolithium reagent has to be used in an amount of approximately 2.2 equivalents based on N-protected amino acid ester. Further, the protecting group of the amino group used in Examples thereof is only a methoxycarbonyl group. However, a method in which elimination of the methoxycarbonyl group is conducted while maintaining a halogenated ketone moiety is unknown. Thus, it is unclear whether the method can be used in the production of an xcex1-aminohalomethylketone.
The invention aims to provide a process for producing an xcex1-aminohalomethylketone and its related compounds which is suited for industrial production, economical and efficient.
The present inventors have assiduously conducted investigations to solve the problems, and have consequently found that a novel N-protected-xcex1-aminohalomethylketone is obtained in high yield by protecting an amino group of an xcex1-amino acid ester as an imine (Schiff base) and then reacting it with a halomethyllithium.
Further, it has been found that this N-protected-xcex1-aminohalomethylketone is easily deprotected through the treatment with an acid to form an xcex1-aminohalomethylketone.
This xcex1-aminohalomethylketone can be converted into an N-protected-xcex2-aminoepoxide via an N-protected-xcex1-aminohalomethylketone and an N-protected-xcex2-aminoalcohol.
Moreover, the inventors have found a process for producing an N-protected-xcex2-aminoepoxide from an xcex1-aminohalomethylketone via a xcex2-aminoalcohol and an N-protected-xcex2-aminoalcohol.
Besides, the inventors have found a method in which an amino group of an xcex1-aminohalomethylketone is protected with a carbamate group (especially a tert-butoxycarbonyl group).
The inventors have completed the invention based on these findings.
That is, the invention provides a process for producing an xcex1-aminohalomethylketone represented by formula (3) 
wherein
A represents an optionally substituted alkyl group having 1 to 10 carbon atoms, an optionally substituted aryl group having 6 to 15 carbon atoms, an optionally substituted aralkyl group having 7 to 20 carbon atoms, or a group in which heteroatom is contained in these carbon skeletons, and
X represents a halogen atom
or its salt, which comprises reacting an N-protected-xcex1-amino acid ester represented by formula (1) 
wherein
R1 and R2, independently from each other, represent an optionally substituted aryl group or lower alkyl group, or a hydrogen atom,
R3 represents an optionally substituted lower alkyl group, aralkyl group or aryl group, and
A is as defined above,
provided R1 and R2 may together form a ring structure with a halomethyllithium, and then treating this with an acid.
The invention is described in detail below.
In the formula in the invention, R1 and R2, independently from each other, represent an optionally substituted aryl group or lower alkyl group, or a hydrogen atom. R1 and R2 may together form a ring structure directly or through an appropriate group. The substituent in the optionally substituted group is not particularly limited so long as it does not have an adverse effect on the reaction of the invention in particular. Examples thereof can include an alkoxy group (preferably having 1 to 6 carbon atoms), a nitro group, an alkyl group (preferably having 1 to 6 carbon atoms) and a halogen atom.
An aryl group is preferably an optionally substituted phenyl group, especially preferably a phenyl group, a p-methoxyphenyl group or a p-isopropylphenyl group. A lower alkyl group includes a linear or branched saturated alkyl group having 1 to 4 carbon atoms.
When the ring structure is formed, examples of formulas (16) and (17) can be listed. 
These formulas include a protecting group moiety formed from R1 and R2 and an imine structure.
It is preferable that both of R1 and R2 are optionally substituted aryl groups, or that one thereof is an optionally substituted aryl group and the other is a hydrogen atom.
In the formula in the invention, R3 is (i) an optionally substituted lower alkyl group or aralkyl group, or (ii) an optionally substituted aryl group. Examples thereof can include an optionally substituted linear or branched saturated alkyl group having 1 to 8 carbon atoms, an optionally substituted aralkyl group having 7 to 15 carbon atoms, and an optionally substituted aryl group having 6 to 14 carbon atoms. Especially, a linear or branched saturated alkyl group having 1 to 3 carbon atoms, such as a methyl, ethyl, propyl or isopropyl group, or an optionally substituted benzyl group is preferable. The substituent in the optionally substituted group is not particularly limited so long as it does not have an adverse effect on the reaction of the invention in particular. Examples thereof can include an alkoxy group (preferably having 1 to 7 carbon atoms), a nitro group, an alkyl group (preferably having 1 to 6 carbon atoms) and a halogen atom.
In the formula in the invention, A represents a hydrogen atom, an optionally substituted alkyl group having 1 to 10 carbon atoms, an optionally substituted aryl group having 6 to 15 carbon atoms, an optionally substituted aralkyl group having 7 to 20 carbon atoms, or a group in which heteroatom is contained in these carbon skeletons. The substituent in the optionally substituted group is not particularly limited so long as it does not have an adverse effect on the reaction of the invention in particular. Examples thereof can include an alkoxy group (preferably having 1 to 6 carbon atoms), a nitro group, an alkyl group (preferably having 1 to 6 carbon atoms) and a halogen atom.
Examples of the group in which the heteroatom (for example, nitrogen, oxygen or sulfur atom) is contained in the carbon skeletons include methylthioethyl, tert-butylthiomethyl, tritylthiomethyl (p-methylbenzyl)thiomethyl, (p-methoxybenzyl)thiomethyl, tert-butoxymethyl, benzyloxymethyl, tert-butoxyethyl, benzyloxyethyl, 4-(tert-butoxy)phenylmethyl, 4-benzyloxyphenylmethyl and phenylthiomethyl groups.
This group can be introduced using, for example, an amino acid as a starting material. For example, it can be introduced using, as a starting material, glycine when A is a hydrogen atom, alanine when A is a methyl group, valine when A is an isopropyl group, leucine when A is a 2-methylpropyl group, isoleucine when A is a 1-methylpropyl group, phenylalanine when A is a benzyl group, or methionine when A is a methylthioethyl group.
A may be a group introduced by using, as a starting material, an amino acid with a functional group of an amino acid side chain protected, examples thereof being S-tert-butylcysteine, S-tritylcysteine, S-(p-methylbenzyl)cysteine, S-(p-methoxybenzyl)cysteine, O-tert-butylserine, O-benzylserine, O-tert-butylthreonine, O-benzylthreonine, O-tert-butyltyrosine and O-benzyltyrosine.
A is not limited to a group introduced from a starting material derived from a natural amino acid, and it may be a group introduced from a starting material derived from an artificial amino acid (for example, a phenyl group or a phenylthiomethyl group).
A is preferably a benzyl group or a phenylthiomethyl group.
In the formula in the invention, X represents a halogen atom. Examples of the halogen atom include fluorine, chlorine, bromine and iodine atoms. A chlorine or bromine atom is preferable, and a chlorine atom is especially preferable.
In the formula in the invention, B1 and B3, independently from each other, represent a protecting group of an amino group. The protecting group of the amino group is not particularly limited. For example, protecting groups described in Protecting Groups in Organic Chemistry, 2nd edition, John Wiley and Sons, Inc. 1991 can be used. Of these, a carbamate-type protecting group (B2 in the invention) is used especially preferably because it is easily removed. Examples of the carbamate-type protecting group include methoxycarbonyl, ethoxycarbonyl, tert-butoxycarbonyl, benzyloxycarbonyl, fluorenylmethoxycarbonyl and tetrahydrofuran-3-yloxycarbonyl groups.
These protecting groups are not necessarily eliminated, and they are sometimes used without being eliminated according to the subsequent step or the desired compound. Examples thereof include a tetrahydrofuran-3-yloxycarbonyl group (refer to EP 774453) and a 3-protected-hydroxy-2-methylbenzoyl group.
The N-protected-xcex1-amino acid ester represented by formula (1), which is used as a starting material in the invention, can easily be produced, as schematically shown below, by a known method from an xcex1-amino acid ester represented by formula (4) or its salt and an imine compound represented by formula (5) or an aldehyde or ketone compound represented by formula (6). 
wherein R1, R2, R3 and A are as defined above.
When the amino acid ester and the aldehyde compound are reacted, these can be reacted in the presence of a dehydrating agent such as anhydrous sodium sulfate, anhydrous magnesium sulfate, calcium chloride or a molecular sieve or an acid (refer to, for example, A. Dondoni et al., Synthesis 1993, 1162). Examples of the solvent at this time can include aprotic solvents such as dichloromethane, chloroform, tetrahydrofuran, ether, tert-butylmethyl ether, toluene, ethyl acetate and isopropyl acetate. When the amino acid ester salt is used as a starting material, it may be used in the reaction by neutralization with the addition of 1 equivalent of a base to the reaction system. Also when the amino acid ester and the ketone compound are reacted, the reaction can be conducted by the same method as in the aldehyde compound (refer to, for example, M. J. O""Donnell et al., Tetrahedron Lett. 1978, 30, 2641).
When the amino acid ester and the imine compound are reacted, the amino acid ester salt and the imine compound can be reacted using the same reaction solvent as mentioned above (refer to, for example, M. J. O""Donnell et al., J. Org. Chem. 1982, 47, 2663).
Preferable examples of the imine compound represented by formula (5) can include benzophenonimine and 9-fluorenonimine. Preferable examples of the aldehyde or ketone compound represented by formula (6) can include benzaldehyde, anisaldehyde, cuminaldehyde and p-nitrobenzaldehyde. Such compounds can be procured industrially at low costs.
The process of the invention can be applied to the synthesis of optically active compounds using optically active xcex1-amino acid esters obtained by esterifying optically active amino acids. The optically active amino acids are important in the medical use. That is, as the xcex1-amino acid esters, optically active compounds (L-isomers or D-isomers) are preferably used. Especially, optically active phenylalanine esters and optically active phenylthioalanine esters are important as starting materials of HIV protease inhibitors.
Next, a process for producing an N-protected-xcex1-aminohalomethylketone represented by formula (2) by reacting the N-protected-xcex1-amino acid ester represented by formula (1) with a halomethyllithium is described. 
wherein R1, R2, A and X are as defined above.
The halomethyllithium in the invention can be represented by formula (19).
Lixe2x80x94CH2xe2x80x94Xxe2x80x83xe2x80x83(19) 
wherein X is as defined above.
Such a halomethyllithium can be formed by the reaction of an organolithium compound such as methyllithium, n-butyllithium or sec-butyllithium with a dihalomethane such as bromochloromethane, chloroiodomethane or dibromomethane (refer to, for example, Encyclopedia of Reagents for Organic Synthesis, John Wiley and Sons, Inc. 1995). A halomethylketone can be obtained by reacting the thus-formed halomethyllithium with an ester (refer to, for example, R. Tarhouni et al., Tetrahedron Lett. 1984, 25, 835, and J. Barluenga et al., J. Chem. Soc., Chem. Commun. 1994, 969). In the invention also, it is advisable that the organolithium compound and the dihalomethane are added to a reaction solvent and the halomethyllithium is formed in the reaction system.
Preferable examples of the halomethyllithium include chloromethyllithium and bromomethyllithium, and chloromethyllithium is especially preferable. When xcex1-aminochloromethylketone (X is a chlorine atom in formula (3)) is produced, chloromethyllithium is formed. When xcex1aminobromomethylketone (X is a bromine atom in formula (3)) is produced, bromomethyllithium is formed.
Since it is known that the halomethyllithium is thermally unstable, it is preferable that when the halomethyllithium and the ester are reacted, the ester and the dihalomethane are previously dissolved in a solvent and the organolithium compound is then added. Further, at this time, a salt such as lithium chloride or lithium bromide may be present.
The organolithium compound used in the invention can be represented by, for example, formula (18).
R4xe2x80x94Lixe2x80x83xe2x80x83(18) 
wherein R4 represents a lower alkyl group, or an aryl group.
The lower alkyl group can include a linear or branched saturated alkyl group having 1 to 8 carbon atoms. Examples of the aryl group can include a phenyl group and a naphthyl group. A lower alkyllithium in which R4 is a lower alkyl group is preferable. It is especially preferable that R4 is a linear saturated alkyl group having 1 to 6 carbon atoms, such as a methyl, ethyl, n-butyl or n-hexyl group.
Preferable examples of the dihalomethane used in the invention include bromochloromethane, chloroiodomethane and dibromomethane, and bromochloromethane and chloroiodomethane are especially preferable. When an xcex1-aminochloromethylketone (X is a chlorine atom in formula (3)) is produced (when chloromethyllithium is formed), bromochloromethane and chloroiodomethane are used. When xcex1-aminobromomethylketone (X is a bromine atom in formula (3)) is produced (when bromomethyllithium is formed), dibromomethane is used.
The amounts of the organolithium compound and the dihalomethane are not particularly limited. It is advisable that each of them may be used in an amount of 1 to 2 equivalents based on the N-protected-xcex1-amino acid ester derivatives. Of course, more than 2 equivalents may be used. However, these reagents are costly. In the invention, it is preferably between 1 and 1.5 equivalents, more preferably between 1.2 and 1.4 equivalents.
As the reaction solvent, ether-type solvents such as tetrahydrofuran, diethyl ether and tert-butylmethyl ether are preferable. Further, mixed solvents of these solvents and nonpolar solvents such as toluene and hexane are also preferable. The reaction proceeds quickly at a temperature of xe2x88x92120xc2x0 C. to 0xc2x0 C. The reaction is conducted preferably in the range of xe2x88x9280xc2x0 C. to xe2x88x9250xc2x0 C. Usually, the reaction is completed in 5 to 60 minutes. After the completion of the reaction, it is advisable that the reaction solution is treated with an ammonium chloride aqueous solution, a phosphate buffer solution or water. Further, when the reaction solution is treated with an acid, a hydrolysis reaction of an imine (Schiff base) in the subsequent step can directly be conducted.
The resulting N-protected-xcex1-aminohalomethylketone (2) can be used through purification by a method known to those skilled in the art, such as column chromatography or crystallization. However, as stated earlier, it may be used in the subsequent reaction without purification by separation.
A process for producing an xcex1-aminohalomethylketone represented by formula (3) by treating the N-protected-xcex1-aminohalomethylketone represented by formula (2) with an acid is described below.
The imine (Schiff base) moiety of the N-protected-xcex1-aminohalomethylketone represented by formula (2) can easily be hydrolyzed with an acid.
The acid used is not particularly limited. Examples thereof can include inorganic acids such as hydrochloric acid, hydrobromic acid, hydroiodic acid, sulfuric acid and phosphoric acid, and organic acids such as trifluoroacetic acid, methanesulfonic acid, benzenesulfonic acid and p-toluenesulfonic acid.
The solvent is not particularly limited. Examples thereof include water, methanol, ethanol, tetrahydrofuran, dioxane, ethyl acetate, isopropyl acetate, dichloromethane, chloroform, toluene, hexane, and mixed solvents of these.
After water is added to the reaction solution, an aldehyde or a ketone as a by-product of hydrolysis can be removed to an organic layer by washing an aqueous layer with an appropriate organic solvent such as ethyl acetate, isopropyl acetate, dichloromethane, chloroform or toluene. The resulting aqueous layer is concentrated, an insoluble matter is filtered off with the addition of an alcohol, and crystallization (for example, crystallization by cooling or crystallization by concentration) is conducted from an alcohol or a mixed solvent of an alcohol and another solvent under appropriate conditions, whereby an xcex1-aminohalomethylketone can be obtained as a salt. Preferable examples of the alcohol include methanol, ethanol and 2-propanol. Examples of the solvent used in combination with the alcohol include ethyl acetate, isopropyl acetate, dichloromethane, ether, tert-butylmethyl ether, tetrahydrofuran, 1,4-dioxane, benzene, toluene and water.
Various xcex1-aminohalomethylketone salts are prepared according to acids used. These salts can be used as such in the subsequent reaction in the invention. Free compounds can be formed by reacting the salts with an equivalent amount of a base. However, the free compounds are unstable compared with the salts. Thus, it is preferable that the salts are used in the form of acid salts as such.
When an alkoxycarbonylation reaction (for example, methoxycarbonylation, ethoxycarbonylation, tert-butoxycarbonylation or benzyloxycarbonylation) of the xcex1-aminohalomethylketone or a reduction reaction of a carbonyl group is conducted in the subsequent step, the aqueous layer can be used in the reaction in the next step directly or as required, by distilling off the solvent without conducting crystallization or purification by separation.
A process for producing an N-protected-xcex1-aminohalomethylketone represented by formula (7) by protecting the amino group of the xcex1-aminohalomethylketone represented by formula (3) with the protecting group is described below. 
wherein A, X and B1 are as defined above.
The xcex1-aminohalomethylketone is stable under acidic conditions but unstable under basic conditions. Therefore, it is undesirable that the reaction is conducted under basic conditions which are ordinarily applied to the protection reaction of the amino group in the peptide synthesis.
That is, an amino group protecting reagent such as an alkoxycarbonylation reagent, an acylation reagent or a sulfonylation reagent has to act in the presence of a base. At this time, decomposition of the xcex1-aminohalomethylketone in not a small amount proceeds to invite the decrease in the reaction yield. Accordingly, to protect the same in good yield, it is advisable to conduct the protection by either of the two procedures mentioned below.
Procedure 1: The amino group protecting reagent such as an alkoxycarbonylation reagent, an acylation reagent or a sulfonylation reagent and a base are mixed in an appropriate solvent, and a solution of an xcex1-aminohalomethylketone acid salt is then added thereto.
Procedure 2: A solution of the amino group protecting reagent such as an alkoxycarbonylation reagent, an acylation reagent or a sulfonylation reagent and a solution of an xcex1-aminohalomethylketone acid salt are mixed, and a base is then added thereto.
The alkoxycarbonylation (carbamation) of the xcex1-aminohalomethylketone here referred to is a novel process, and the procedure 1 is also a novel process. Especially when tert-butoxycarbonylation is conducted, it is advisable to follow the procedure 1 because tert-butoxycarbonyl chloride or di-tert-butyl dicarbonate as the protecting reagent is unstable to an acid. That is, the procedure 1 is quite an excellent method in the tert-butoxycarbonylation reaction of the xcex1-aminohalomethylketone in particular.
In the xcex1-aminohalomethylketone, it is advisable to use the above-described stable acid salt. Examples of an appropriate solvent for dissolving the acid salt can include water, methanol and ethanol, for example.
The amino group protecting reagent is not particularly limited. A reagent ordinarily used in the peptide synthesis can of course be used, and further an optional compound having a functional group such as an alkoxycarbonyl group, an acyl group or a sulfonyl group can be used for introducing an optional substituent.
Examples of the amino acid protecting reagent can include alkoxycarbonylation reagents such as methoxycarbonyl chloride, ethoxycarbonyl chloride, isopropoxycarbonyl chloride, tert-butoxycarbonyl chloride, benzyloxycarbonyl chloride, di-tert-butyl dicarbonate and tetrahydrofuran-3-yloxycarbonyl chloride, acylation reagents such as acetic anhydride, acetyl chloride, benzoyl chloride and 3-protected hydroxy-2-methylbenzoyl chloride, and sulfonylation reagents such as methanesulfonyl chloride, trifluoromethanesulfonyl chloride, benzenesulfonyl chloride and p-toluenesulfonyl chloride. As stated earlier, the protecting groups introduced with these protecting reagents are sometimes not eliminated according to the subsequent step or the desired compound.
Examples of the base include organic bases such as triethylamine, diisopropylethylamine, dicyclohexylmethylamine, N-methylmorpholine, N-ethylmorpholine, pyridine, 2,6-lutidine, 2,4,6-collidine, 4-picoline and N-ethylpiperidine, and inorganic bases such as sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium hydrogencarbonate, potassium hydrogencarbonate, disodium hydrogenphosphate and dipotassium hydrogenphosphate.
With respect to the reaction solvent, an appropriate solvent can be used according to the reagent. Examples thereof include water, methanol, ethanol, 2-propanol, tert-butanol, acetone, tetrahydrofuran, diethyl ether, tert-butylmethyl ether, ethyl acetate, isopropyl acetate, dichloromethane, chloroform, toluene and mixed solvents thereof. When mixed solvents are used, there are a single layer system and a two-layer system depending on a combination of solvents. It is especially preferable that the reaction is conducted with a two-layer system through stirring.
When the amino group protecting reagent and the base are mixed in an appropriate solvent and a solution of an xcex1-aminohalomethylketone acid salt is then added thereto (procedure 1), sodium hydrogencarbonate, potassium hydrogencarbonate, triethylamine or diisopropylethylamine is preferably used as the base. Triethylamine and diisopropylethylamine are especially preferable. The amount of the base to be added to the solution of the protecting reagent is preferably between 0.8 and 1.2 equivalents, more preferably close to 1 equivalent based on an acid (including an acid participating in formation of a salt) present in the xcex1-aminohalomethylketone acid salt solution.
The xcex1-aminohalomethylketone solution is added to the solvent in which the protecting reagent is dissolved. The reaction time varies with the reagent used or the reaction temperature. For example, when the tert-butoxycarbonylation is conducted with di-tert-butyl dicarbonate, the reaction is completed at 40xc2x0 C. in several minutes to 2 hours and at room temperature in several minutes to 10 hours.
When the solution of the amino group protecting reagent such as the alkoxycarbonylation reagent, the acylation reagent or the sulfonylation reagent and the solution of the xcex1-aminohalomethylketone acid salt are mixed and the base is then added thereto (procedure 2), sodium hydrogencarbonate, potassium hydrogencarbonate, triethylamine or diisopropylethylamine is preferably used as the base. The amount of the base added at this time is preferably between 0.8 and 1.2 equivalents, more preferably close to 1 equivalent based on an acid (including an acid participating in the formation of a salt) present in the xcex1-aminohalomethylketone acid salt solution.
The base is added by being dissolved in an appropriate solvent. The reaction time varies with the reagent used or the reaction temperature. When the benzyloxycarbonylation is conducted using benzyloxycarbonyl chloride and the reaction is conducted at room temperature, the reaction is completed in 10 minutes to 2 hours.
Subsequently, the reaction solution is extracted with a solvent such as ethyl acetate, diethyl ether, toluene, isopropyl acetate, tert-butylmethyl ether, dichloromethane or chloroform, and the solution is concentrated (or distilled off) as required. Then, a solvent such as methanol, ethanol, 2-propanol, acetonitrile, tetrahydrofuran, hexane, heptane or acetone is added as required, the solution is heated to between 40xc2x0 C. and 80xc2x0 C., and crystallization is conducted by cooling to between xe2x88x9220xc2x0 C. and room temperature or chromatography is conducted. In this manner, the N-protected-xcex1-aminohalomethylketone (7) can be obtained as a solid. Further, the product may be used in the next reaction without purification by separation.
The N-protected-xcex1-aminohalomethylketone represented by formula (7) is a known compound which is useful as, for example, an intermediate of a HIV protease inhibitor (refer to, for example, D. P. Getman et al., J. Med. Chem., 1993, 36, 288, Y. Okada et al., Chem. Pharm. Bull., 1988, 36, 4794, EP 346867 and P. Raddatz et al., J. Med. Chem., 1991, 34, 3267). It is known that the compound is converted into an intermediate in an advanced form by, for example, the following two-step known method (refer to, for example, D. P. Getman et al., J. Med. Chem., 1993, 36, 288, WO96/23756 and Japanese Patent Laid-Open Nos. 99,947/1996 and 99,959/1996).
That is, it is possible that the N-protected-xcex1-aminohalomethylketone represented by formula (7) is converted into an N-protected-xcex2-aminoalcohol represented by formula (8) by a reduction reaction of a carbonyl group and this alcohol is further epoxidized easily under alkaline conditions to form an N-protected-xcex2-aminoepoxide represented by formula (9). 
wherein A, X and B1 are as defined above.
An example using sodium borohydride as a reducing agent is described below.
The amount of sodium borohydride added is not particularly limited. It is ordinarily used in an amount of 0.5 mol equivalent or more based on the starting material.
Examples of the reaction solvent can include protonic solvents such as water and alcohol. An alcohol or a mixed solvent of an alcohol and one or more of the other solvents is preferably used. Examples of the alcohol include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol and 1,2-dimethylpropanol. Methanol and ethanol are especially preferable. Further, as an alcohol, a combination of these is also available. Examples of the solvent used by being mixed with the alcohol include ethyl acetate, isopropyl acetate, dichloromethane, ether, tert-butylmethyl ether, tetrahydrofuran, 1,4-dioxane, benzene, toluene and water. Ethyl acetate, toluene and water are especially preferable.
The reaction temperature is not particularly limited. It is usually room temperature or less, preferably between xe2x88x9278xc2x0 and room temperature, more preferably between xe2x88x9278xc2x0 C. and 5xc2x0 C. The reaction time is not particularly limited either. It is preferably between 10 minutes and 10 hours.
The reaction is usually conducted with stirring. After the completion of the reaction, the reaction is usually terminated with the addition of an acid. As the acid, hydrochloric acid, sulfuric acid, acetic acid, citric acid or a potassium hydrogensulfate aqueous solution can preferably be used. The amount of the acid used is not particularly limited. It is preferably used in an amount of 1 equivalent or more based on sodium borohydride.
Subsequently, the reaction solution is extracted with a solvent such as ethyl acetate, diethyl ether, toluene, isopropyl acetate, tert-butylmethyl ether, dichloromethane or chloroform, and the solution is concentrated (or distilled off) as required. Then, a solvent such as methanol, ethanol, 2-propanol, acetonitrile, tetrahydrofuran, hexane, heptane or acetone is added as required, the solution is heated to between 40xc2x0 C. and 80xc2x0 C., and crystallization is conducted by cooling to between xe2x88x9220xc2x0 C. and room temperature or chromatography is conducted. In this manner, the N-protected-xcex2-aminoalcohol can be obtained as a solid. Further, the crystals of the N-protected-xcex2-aminoalcohol can also be obtained by concentrating the reaction solution as required, adding water thereto as required, directly conducting the crystallization by cooling under the above-mentioned conditions and washing the resulting crystals with water or the organic solvent.
The N-protected-xcex2-aminoepoxide represented by formula (9) can be produced by treating the resulting N-protected-xcex2-aminoalcohol represented by formula (8) with a base.
Examples of the base include potassium hydroxide, sodium hydroxide, potassium carbonate, sodium carbonate, sodium methoxide, sodium ethoxide, potassium tert-butoxide and sodium hydride. Sodium hydroxide and potassium carbonate are especially preferable. Examples of the reaction solvent include protonic solvents such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 1,2-dimethylpropanol and water, and aprotic solvents such as acetone, tetrahydrofuran and acetonitrile. These are used either singly or in combination. Ethanol, a mixed solvent of 2-propanol and water, and a mixed solvent of ethanol and water are especially preferable.
The amount of the base used varies with the combination of the base and the solvent used. It is between 1 and 10 equivalents, preferably between 1 and 5 equivalents. The reaction temperature also varies with the combination of the base and the solvent used. It is between xe2x88x9210 and 80xc2x0 C., preferably between 0 and 60xc2x0 C. The reaction time is not particularly limited, and it is preferably between 10 minutes and 50 hours.
The reaction is usually conducted with stirring. After the completion of the reaction, the reaction may be terminated with the addition of an acid. As the acid, hydrochloric acid, sulfuric acid, acetic acid, citric acid or a potassium hydrogensulfate aqueous solution can preferably be used.
Subsequently, the reaction solution is extracted with a solvent such as ethyl acetate, diethyl ether, toluene, isopropyl acetate, tert-butylmethyl ether, dichloromethane or chloroform, and the solution is concentrated as required. Then, a solvent such as methanol, ethanol, 2-propanol, acetonitrile, tetrahydrofuran, hexane, heptane or acetone is added as required, the solution is heated to between room temperature and 50xc2x0 C. as required, and crystallization is conducted by cooling to between xe2x88x9220xc2x0 C. and room temperature or chromatography is conducted. In this manner, the N-protected-xcex2-aminoepoxide can be obtained as a solid. Further, the crystals of the N-protected-xcex2-aminoepoxide can also be obtained by concentrating the reaction solution as required, adding water thereto as required, directly conducting the crystallization by cooling under the above-mentioned conditions and washing the resulting crystals with water or the organic solvent.
The N-protected-xcex2-aminoalcohol can also be formed from the xcex1-aminohalomethylketone represented by formula (3) via the following novel route. 
wherein A, B3 and X are as defined above.
That is, the N-protected-xcex2-aminoalcohol represented by formula (14) can be obtained by reducing the carbonyl group of the xcex1-aminohalomethylketone represented by formula (3) to form a xcex2-aminoalcohol represented by formula (13) and then protecting the amino group with a protecting group.
A reducing agent is previously dissolved or suspended in an appropriate solvent, and a solution of an acid salt of the xcex1-aminohalomethylketone is added thereto.
The solvent in which the reducing agent is dissolved or suspended is not particularly limited. Protonic solvents such as water, methanol and ethanol are preferable.
Examples of the solvent in which the xcex1-aminohalomethylketone is dissolved include water, methanol and ethanol. The xcex1-aminohalomethylketone is preferably used in the form of a salt with an acid.
The reducing agent is not particularly limited. When it is reacted in an aqueous solution, sodium borohydride and sodium boron cyanohydride are especially preferable. The amount of the reducing agent added is not particularly limited. It is ordinarily used in an amount of 0.5 mol equivalent or more based on the starting material.
For inhibiting decomposition of the reducing agent with the acid, it is preferable to previously add a base along with the reducing agent. The amount of the base added to the solution of the reducing agent at this time is preferably between 1 and 2 equivalents, more preferably close to 1 equivalent based on the acid (including an acid participating in the formation of a salt) present in the acid salt solution of the xcex1-aminohalomethylketone.
Examples of the base include sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium hydrogencarbonate and potassium hydrogencarbonate.
The reaction time is not particularly limited. When, for example, sodium borohydride is used, the reaction is conducted preferably at xe2x88x9220xc2x0 C. to 100xc2x0 C., especially preferably at 0xc2x0 C. to room temperature.
The reaction is usually conducted with stirring. After the completion of the reaction, the reaction is terminated with the addition of an acid. As the acid, hydrochloric acid, sulfuric acid, acetic acid, citric acid or a potassium hydrogensulfate aqueous solution can preferably be used. The amount of the acid used is not particularly limited. It is preferably used in an amount of 1 equivalent or more based on sodium borohydride.
An insoluble matter is filtered off with the addition of an alcohol, and thereafter, crystallization (for example, crystallization by cooling or crystallization by concentration) is conducted from an alcohol or a mixed solvent of an alcohol and one or more of other solvents under appropriate conditions, whereby a xcex2-aminoalcohol can be obtained as a salt. Preferable examples of the alcohol include methanol, ethanol and 2-propanol. Examples of the solvent used by being mixed with the alcohol include ethyl acetate, isopropyl acetate, dichloromethane, diethyl ether, tert-butylmethyl ether, tetrahydrofuran, 1,4-dioxane, benzene, toluene and water.
The xcex2-aminoalcohol represented by formula (13) is a known compound which is useful as, for example, an intermediate of a HIV protease inhibitor (refer to, for example, P. L. Beaulieu et al., J. Org. Chem., 1996, 61, 3635). It is known that the compound is converted into an intermediate in an advanced form through, for example, the following two-step known reaction.
That is, it is possible that the xcex2-aminoalcohol represented by formula (13) is converted into the N-protected-xcex2-aminoalcohol represented by formula (14) by protecting the amino group in the foregoing manner and this alcohol is easily epoxidized under alkaline conditions as described above to form the N-protected-xcex2-aminoepoxide represented by formula (15).
In the process of the invention, the protecting group such as the alkoxycarbonyl group, the acyl group or the sulfonyl group can be introduced into the xcex1-aminohalomethylketone represented by formula (3) at good efficiency. That is, it is a general-purpose excellent process which can introduce a protecting group suited to a process for synthesis of various medical compounds.
The compound in the invention also includes a racemic compound and both optically active compounds. When an optically active amino acid ester is here used as the amino acid ester of formula (4), the compound of formula (3) obtained by the process of the invention maintains its optical activity. Further, in the compounds of formulas (7) to (9) and (13) to (15) produced from the compound of formula (3), the optical activity can also be maintained.
In view of the foregoing, the process of the invention is a process which is quite useful as a process for synthesis of medical intermediate compounds.
The invention is illustrated more specifically by referring to the following Examples. Of course, the invention is not limited to these Examples at all.